1. Field of Invention
The present invention relates to generators, and more particularly to a high efficiency portable generator having a lightweight and compact size for easy storage and carrying.
2. Description of Related Arts
Various kinds of well known portable generator are developed such as U.S. Pat. Nos. 4,595,841, 5,093,611, 4,647,835, 5,555,853, and etc. Conventional portable generator comprises an engine and an alternator (or generator) directly connected to and driven by the engine to generate electricity.
The spark-ignited combustion engine produces mechanical power to drive a crankshaft to rotate. The crankshaft is connected with a revolving shaft of the generator which can induce electrical current by transforming the mechanical power produced from the engine into electrical energy due to the relative movement between a magnetic field and electrically conductive elements.
However, the aforesaid conventional portable generators are not practically portable because of their heavy weight and large size. They claim portable simply because they have incorporated a carrying means. Such as, U.S. Pat. No. 5,555,853 provides a back-pack for carrying the engine/alternator unit; U.S. Pat. No. 4,647,835 provides a box casing with handle for carrying the portable generator. In fact, the conventional portable generator is difficult to be transported in a car trunk and is hard to be carried by a female or a junior with one hand. Generally, more than half of the weight of the conventional portable generator is the alternator; more than half of the size of the conventional portable generator is the alternator too.
In order to produce undirectional cooling air for cooling the engine and the alternator, cooling fans are installed to cool the engine and the alternator respectively. U.S. Pat. No. 4,647,835 suggests how to incorporate a single cooling fan at the connection portion of a crankshaft in the engine and a revolving shaft in the alternator (generator). The cooling fan(s) not only increases the size of the portable generator, but also increase the weight of the portable generator.
Moreover, the conventional structure of the alternator/generator is also relatively complicated. A revolving shaft, supported by bearings, is extended through the alternator from the crankshaft either to connect and drive the rotor with permanent magnets to coaxially rotate within the stator inductor, or to connect and drive the rotor with permanent magnets around the stator inductor. However, these elongated shaft, supporting bearings, and shells unnecessarily increase the weight and size of the conventional portable generator.